Filter media, composites, and face mask systems using same

This application is the § 371 U.S. National Stage of International Application No. PCT/US2021/025676, filed 2 Apr. 2021, which claims the benefit of U.S. Provisional Application No. 63/004,464, filed 2 Apr. 2020, of U.S. Provisional Application No. 63/004,621, filed 3 Apr. 2020, of U.S. Provisional Application No. 63/004,926, filed 3 Apr. 2020, of U.S. Provisional Application No. 63/004,939, filed 3 Apr. 2020, of U.S. Provisional Application No. 63/004,954, filed 3 Apr. 2020, of U.S. Provisional Application No. 63/024,894, filed 14 May 2020, of U.S. Provisional Application No. 63/042,943, filed 23 Jun. 2020, of U.S. Provisional Application No. 63/081,143, filed 21 Sep. 2020, and of U.S. Provisional Application No. 63/081,159, filed 21 Sep. 2020, the disclosures of each of which are incorporated by reference herein in their entireties.

Mask filters including face masks are designed to greatly reduce or prevent the transmission of liquids and/or airborne contaminants to a wearer from the ambient atmosphere. In medical environments, liquid sources may include respiratory droplets (for example, mucus), bodily fluids (for example, perspiration), saline, etc. Examples of potentially airborne contaminants include, for example, biological contaminants such as bacteria, viruses, fungal spores, etc.

This disclosure describes filter media, composites including filter media, and mask filters including those filter media.

As used herein, “fine fiber” refers to a fiber having a diameter of up to 10 micrometers (μm). In some embodiments, a fine fiber has a diameter of at least 50 nm or at least 100 nm.

As used herein, micron is equivalent to micrometer (μm).

As used herein, a “fiber” has an average fiber diameter of up to 100 micrometers. As used herein, fibers having an “average” diameter indicates that in a sample of a plurality of fibers, the average fiber diameter of that population of fibers in that sample has the indicated average fiber diameter. A population of fibers includes fibers having a diameter within 25% of an average fiber diameter. For example, a population of fibers having an average diameter of 1000 nm includes fibers having a diameter of at least 750 nm and up to 1250 nm. In another example, a population of fibers having an average diameter of 250 nm includes fibers having a diameter of at least 188 nm and up to 313 nm. In a further example, a population of fibers having an average diameter of 500 nm includes fibers having a diameter of at least 375 nm and up to 625 nm. In yet another example, a population of fibers having an average diameter of 1400 nm includes fibers having a diameter of at least 1050 nm and up to 1750 nm. Further, “fibers,” as used herein, have an aspect ratio (that is, length to lateral dimension) of greater than 3:1, and preferably greater than 5:1. For example, fiberglass may have an aspect ratio of greater than 100:1. In this context, the “lateral dimension” is the width (in 2 dimensions) or diameter (in 3 dimensions) of a fiber. The term “diameter” refers either to the diameter of a circular cross-section of as fiber, or to a largest cross-sectional dimension of a non-circular cross-section of a fiber. Fiber lengths may be of finite lengths or infinite lengths, depending on the desired result.

Fiber diameter may be measured using a top-down SEM image. The sample may be sputter-coated. A useful sputter-coater may be a gold and palladium mixture including, for example, a Au:Pd 60:40 mixture. A more accurate fiber diameter measurement may be obtained by measuring the diameter of the fiber in at least 30 locations in the sample. Software such as a Trainable Weka Segmentation (an ImageJ plug-in) may be useful for analyzing fiber diameters.

A “mask filter” is defined as a filter element that is configured to filter the air flowing to a face receptacle defined by a face mask. A mask filter may form at least a portion of the face mask itself or may be a filter element that is separate or remote from the face mask and is configured to be in fluid communication with the face receptacle defined by the face mask.

“Face mask” is defined herein as a component that is configured to extend across at least a portion of a wearer's face. A face mask generally defines a face receptacle that is configured to receive at least a portion of a face of a wearer.

A “face mask system” is defined as a system that incorporates a face mask. A “face mask system” may include a face mask alone or a face mask in combination with a mask filter that is separate from the face mask and is configured to be in fluid communication with the face receptacle defined by the face mask. For example, the term “face mask system” includes surgical masks, procedure masks, isolation masks, laser masks, dental masks, patient care masks, filtering facepiece respirators, re-usable respirators including one or more replaceable filter elements, and powered air purifying respirators incorporating one or more filter elements designed to be replaced.

The term “particle size,” as used herein, is refers to a particle's diameter, determined as described in ISO 11171:2016.

As used herein, “continuous fine fiber” refers to a fine fiber having an aspect ratio (that is, length to lateral dimension) of at least 5,000, or, more preferably, at least 10,000. References herein to a continuous fine fiber layer refer to a layer that includes a continuous fine fiber (as opposed to a short cut fine fiber). While a continuous fine fiber layer is preferably formed by a fiber-forming process that produces a continuous fine fiber, the resulting layer may or may not include only one continuous fine fiber. That is, a continuous fine fiber layer may include one or more fine fiber shaving an aspect ratio of at least 5,000, or, more preferably, at least 10,000.

As used herein, “short cut fine fiber” refers to a fine fiber having an aspect ratio (that is, length to lateral dimension) of less than 5,000, less than 2,500, or less than 1,000. Typically, a short cut fine fiber has an aspect ratio of at least 10 and up to 5,000.

As used herein, “commingled” fibers or a “commingled fiber structure” refer to fibers having at least two different diameters, wherein fibers having an average first diameter and fibers having an average second diameter are commingled, that is, wherein fiber are mixed within the same layer (or strata) of a media structure as a result of the fibers having been formed or deposited simultaneously or by using very short (for example, up to 10 seconds, up to 20 seconds, or up to 30 seconds) pulses of each polymer solution. When visualized using a top-down SEM image, fibers having an average first diameter may be observed as being located both below and above fibers having an average second diameter.

As used herein, “layered” fibers or a “layered fiber structure” refer to fibers having at least two different diameters, wherein fibers having an average first diameter are not substantially entangled with the fibers having an average second diameter as a result of fibers of differing diameters having been alternately applied to a substrate.

As used herein, unless indicated otherwise, pore size (for example P5, P50, and P95) and ratios of pore sizes (for example, P95/P50) are determined using capillary flow porometry. Capillary flow porometry may be performed using a continuous pressure scan mode. It may be useful to use silicone oil, having a surface tension of 20.1 dynes/cm and a wetting contact angle of 0, as a wetting liquid. The sample may initially be tested dry, varying low pressure to high pressure, and then tested wet, again varying low pressure to high pressure. The test is typically performed at ambient temperature conditions (for example, 20° C. to 25° C.). 256 data points may be collected across the range of the scan of the pressures for both the dry curve and the wet curve. Typically, no tortuosity factor and/or a shape factor will be used (that is, for comparison to other test methods that use an adjustment factor, a factor equal to 1 may be used).

As used herein, a value P(x %) is the calculated pore size when the wet curve is equal to (100−x) % of the dry curve, as determined using the methodology described herein. Although a calculated value, this can be understood as representing the point at which x % of the overall flow through the layer passes through pores of that size or below. For example, P50 (the mean flow pore size) represents the point at which the wet curve is equal to half the dry curve, and may be viewed as the pore size such that 50% of the total flow through the layer is through pores of that size or below.

An average pore size (for example, average maximum pore size) may be calculated from the mean of at least three measurements (taken from at least three different sample locations. Individual measurements of maximum pore size (which may also be referred to as P100) may be detected at the bubble point, where the bubble point is found after fluid begins passing through the sample, and three consecutive measurements increase by at least 1%, where 256 data points are collected across the scan at a rate of approximately 17 data points per minute.

As used herein, the “β ratio” or “β” is the ratio of upstream particles to downstream particles under steady flow conditions (ISO 16889:2008), as described in the Examples. The more efficient the filter, the higher the β ratio. The β ratio is defined as follows:

where Nis the upstream particle count per unit fluid volume for particles of diameter d or greater and Nis the downstream particle count per unit fluid volume for particles of diameter d or greater. If present, the subscript attached to β indicates the particle size for which the ratio is being reported.

As used herein, “over-all β ratio” or “over-all β” is the ratio of the sum of all upstream particles over the course of the assay to the sum of all downstream particles over the course of the test (where the test is run to a pressure of 25 psi (172 kPa)):

where Nis the upstream particle count per unit fluid volume for particles of diameter d or greater and Nis the downstream particle count per unit fluid volume for particles of diameter d or greater. If present, the subscript attached to β indicates the particle size for which the ratio is being reported.

As used herein, “filtration efficiency” or “efficiency” refers to the percentage of the contaminant removed by the filter, calculated as follows:

where e is the filtration efficiency and β is defined as indicated above. Thus, the efficiencies referred to herein are cumulative efficiencies. If present, the subscript attached to e indicates the particle size for which the ratio is being reported.

As used herein, “pressure drop” (also referred to herein as “dP” or “ΔP”) relates to the pressure (exerted by a pump) necessary to force fluid through the filter or filter medium (prior to the addition of a contaminant) for a particular fluid velocity. Unless otherwise indicated, pressure drop is measured as described in ISO 3968:2017.

The term “substantially free of” as used herein indicates that the filter media does not contain an amount of the listed component (for example, glass fiber or resin) that contributes to the activity or action of the filter media to any substantial extent. The term is intended to include the inclusion of insignificant amounts of the component that do not provide any substantial contribution to the filter media's filtration properties. For example, a filter media that is substantially free of glass may include less than 1 wt-% glass fiber. For example, a filter media that is substantially free of resin may include less than 5 wt-% resin. For example, a filter media that is substantially free of glass may include less than 1 wt-% glass fiber. For example, a filter media that is substantially free of resin may include less than 5 wt-% resin.

The term “free of” as used herein indicates that the filter media does not contain an amount of the listed component (for example, glass fiber or resin). For example, a “glass-free” filter media does not include any glass and a “resin-free” media does not include any resin.

The words “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

The terms “comprises” and variations thereof do not have a limiting meaning where these terms appear in the description and claims. Such terms will be understood to imply the inclusion of a stated step or element or group of steps or elements but not the exclusion of any other step or element or group of steps or elements.

By “consisting of” is meant including, and limited to, whatever follows the phrase “consisting of” Thus, the phrase “consisting of” indicates that the listed elements are required or mandatory, and that no other elements may be present. By “consisting essentially of” is meant including any elements listed after the phrase, and limited to other elements that do not interfere with or contribute to the activity or action specified in the disclosure for the listed elements. Thus, the phrase “consisting essentially of” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present depending upon whether or not they materially affect the activity or action of the listed elements.

Unless otherwise specified, “a,” “an,” “the,” and “at least one” are used interchangeably and mean one or more than one.

As used herein, the term “or” is generally employed in its usual sense including “and/or” unless the content clearly dictates otherwise.

The term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements.

Any reference to standard methods (for example, ASTM, TAPPI, AATCC, ISO, etc.) refers to the most recent available version of the method at the time of filing of this disclosure unless otherwise indicated.

Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (for example, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

Herein, “up to” a number (for example, up to 50) includes the number (for example, 50).

The term “in the range” or “within a range” (and similar statements) includes the endpoints of the stated range.

For any method disclosed herein that includes discrete steps, the steps may be conducted in any feasible order. And, as appropriate, any combination of two or more steps may be conducted simultaneously.

All headings are for the convenience of the reader and should not be used to limit the meaning of the text that follows the heading, unless so specified.

Reference throughout this specification to “one embodiment,” “an embodiment,” “certain embodiments,” or “some embodiments,” etc., means that a particular feature, configuration, composition, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of such phrases in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments.

Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” As used herein in connection with a measured quantity, the term “about” refers to that variation in the measured quantity as would be expected by the skilled artisan making the measurement and exercising a level of care commensurate with the objective of the measurement and the precision of the measuring equipment used. Accordingly, unless otherwise indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. All numerical values, however, inherently contain a range necessarily resulting from the standard deviation found in their respective testing measurements.

The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples may be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list.

While the above-identified figures (which may or may not be drawn to scale) set forth embodiments of the invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments may be devised by those skilled in the art, which fall within the scope of this invention.

In one aspect, this disclosure describes a nonwoven filtration media that includes a fibrous media including bicomponent fibers, glass fibers, and microfibrillated cellulose fibers. In another aspect, this disclosure describes a filter media including an electrostatically charged filter media, a fine fiber layer, and a scrim.

In a further aspect, this disclosure describes a filter media including two fine fiber layers, and two scrims.

In an additional aspect, this disclosure describes a glass-free filtration media and a glass-free composite that includes multiple layers of filtration media. In some embodiments, the filtration media or the composite preferably exhibit capacity and efficiency comparable to or better than similar glass-containing filtration media.

In yet another aspect, this disclosure describes a filter media that includes a support layer and a continuous fine fiber layer.

In some embodiments, the filter media is configured for air filtration.

In some embodiments, the filter media is preferably incorporated in a face mask system having a face mask. As defined above, a “face mask” is a component that is configured to extend across at least a portion of a wearer's face.

In some embodiments, a face mask as described herein may serve as an item of protective clothing designed to protect portions of the wearer's face, including the mucous membrane areas of the wearer's nose or mouth, from contact with airborne contaminants, such as bodily fluids. The face mask may act a barrier for the wearer to a hazard and, additionally or alternatively, the face mask may also act as a barrier that prevents the wearer from becoming a source of contamination.